The present invention relates to ovens with electric heating elements and to electric heating element systems.
Electric cooking ovens for residential use normally have an electric heating element along the bottom wall of the oven and an electric heating element along the top wall or ceiling of the oven, although a recent innovation has employed a gas broiler for the top heating element in an electric oven, as shown in U.S. Pat. No. 5,909,533. Electric cooking ovens are desirable for many reasons, such as the ability to be self-cleaning by developing an extremely high temperature. Conventionally the electric heating element for the bottom of a residential oven has been a Calrod which is supported by a wire frame a short distance above the bottom surface of the oven. The Calrod is an electric resistance heater rod and, when activated, begins to glow and produce heat and some infrared light waves. The Calrod heating element may be open to the oven or in some oven constructions is placed below a steel sheet coated with porcelain enamel that provides a bottom surface of the oven that may be wiped clean without removing the calrod heating element. In older ovens the Calrod element can be removed for cleaning the bottom of the ovens where the Calrod heating element is exposed. However, the porcelain enamel coating often cracks under the high temperatures to which it is subjected, such as by the self-cleaning cycle.
Recently, a ribbon-type heating element has been used as both the top and bottom heating elements in residential ovens because of the more rapid increase in temperature and higher temperature that may be achieved by such a ribbon-type element but the ribbon is susceptible to damage so it must be covered. While a high temperature glass has been used to cover and protect the ribbon-type heating element when used as the upper element, the porcelain enamel metal sheet that is used to protect the ribbon type bottom heating element is highly susceptible to cracks. Moreover, the porcelain enamel coated metal sheet illuminates infrared heating from the bottom element and is a poor heat conductor.
Both as a practical matter and to meet modern safety requirements, the bottom heating element in an electric oven must successfully resist liquid spills and impacts from pans, which has led to the use of the porcelain enamel coated sheet immediately above the bottom heating element which creates the inefficiencies and potential failures noted above. Heretofore a glass cover over the bottom electric heating element has been unacceptable because of the inability to meet the required impact resistance requirements and, to a lesser extent, the liquid spill resistance requirements.